We can import the search configuration for a site collection to replicate the search settings. Can we do the same for tenant level search settings? Or can we change individual property of search configuration for eg Search Center URL using SharePoint online management shell?
The cmdlets for SharePoint Online are very limited and do not allow you to set search settings: https://technet.microsoft.com/en-us/library/fp161364.aspx
You can look towards CSOM solutions on Technet Gallery or CodePlex. There are even some solutions that include additional SPO cmdlets, but I am not familiar with any search-related CMDLETS -> so scripting.
From the user interface you can modify the tenant level Search Settings under this link: https://TENANTNAMECHANGEPLS-admin.sharepoint.com/_layouts/15/searchadmin/TA_SearchAdministration.aspx